change name of previous user to new user

I have a windowxp home edition computer with service pack 2 installed. My son’s name was used when I installed windowsxp. I want to change it to my daughter’s name (my son has his own computer) but in documents and settings, his name appear as a folder. Windows will not let me change the name since it contains system files. Is there a way to change the name of the folder or can I replace the folder completely in my daughter’s name? Please send me any suggestions you have. I look forward to your response. Thanks. MMN